42 /. H. Powers 



from animals shortly after metamorphosis and all were, I believe, 

 males. Figure 7 is from an animal 19 cm. long, figure 8, 21.5 

 cm., and figure 10, 20 cm. Moreover, figures 7 and 10 are from 

 animals taken the same season, at about the same time, and from 

 ponds where the conditions, though different, were thoroughly- 

 normal. Careful observation of animals in aquaria and under 

 different conditions of feeding show the cause to be, here again, 

 one of nutrition, supplemented by the factor, decidedly second- 

 ary in importance, of use or disuse. The differences that may 

 result thus with larvae of the same age, of about the same length, 

 and similarly situated in every way, save as to amount of food or 

 habit of eating, are very great. Correspondnig specimens may 

 show limbs varying in diameter from three to five mm. respect- 

 ively, and thus varying in bulk nearly as five to one. My first 

 observations led me to consider this rapid strengthening of the 

 limbs as a change preparatory for metamorphosis ; for such lar- 

 vae, however beautiful their branchiae, proved usually on the 

 verge of change. However, further study showed that many, if 

 not the majority, metamorphosed with very little of this hyper- 

 trophy of the posterior limb, and that finally the connection of 

 the sudden limb development with metamorphosis was indirect 

 and not direct, the sudden limb development being due to a sud- 

 den excess of nutrition and growth,, and the metamorphosis to 

 the corresponding retardation which is so certain to follow the 

 acceleration. 



We next come to variation in the feet, and especially the toes. 

 Few characters are more interesting, and nowhere have the re- 

 sults of my observations been more surprising to myself. The 

 amount of variation is again ver}^ great, as a glance at the plates, 

 especially plate II and plate IV will show. Baird and Cope de- 

 scribed these variations, and, conformant to their usual principles, 

 ascribed them unhesitatingly to varying degrees of aquatic or 

 terrestrial habit in the adult. . Nothing seems more reasonable — 

 before we study the facts. Then contradiction arises immediately. 

 I secured old adults whose finely and closely scratched skins, to- 

 gether with numerous other features, showed them to have just 

 emerged from long periods of .burrowing life: still they showed 



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